Spacecraft, such as space shuttles, space stations, and satellites have internal environments (e.g., cabins or heat generating components) that are cooled by a coolant loop. The coolant loop circulates a flow of coolant which absorbs heat from the internal environment of the spacecraft. The coolant may absorb heat from the cabin itself, or from other components (such as mechanical or electronic components) associated with the spacecraft. The heat absorbed by the coolant is then rejected to an external environment using a heat sink.
In space applications, the heat sink is known to be provided by a radiator that is located at least partially external to the spacecraft. The effective cold sink provided by outer space varies quite widely depending on spacecraft orientation. This will provide an effective heat sink. As the coolant within the coolant loop flows within the radiator, the heat within the coolant is rejected to outer space. Downstream of the radiator, the coolant is recirculated back to the coolant loop.
The heat rejection capacity of the radiator is fixed by the size of the radiator, the optical property of the radiator surface, and the effective temperature of the radiator surface. The radiator is typically sized to handle an expected upper limit operating temperature and heat load (e.g., a “worst case” operating condition) of the spacecraft. Some other types of radiators allow for variable heat rejection using variable emissivity surface coatings or mechanical louvers.